1. Field of the Invention
The present invention relates to a shock absorber for a two-wheeled vehicle. In particular, the present invention relates to a shock absorber for a two-wheeled vehicle for effectively protecting an occupant against a frontal crash of the two-wheeled vehicle.
2. Description of Background Art
A shock absorber is used in an automotive vehicle for protecting occupants in case of a collision. For example, shock absorbers are provided inside of pillar garnishes for protecting the heads of the occupants and inside of the door trims for protecting the backs or the chests of the occupants and the like in case of a side collision. Resin ribs that can be manufactured at relatively low cost have been in heavy usage as shock absorbers (See JP-A-8-164810, JP Patent No. 2978083, etc.).
However, with regard to two-wheeled vehicles, the absorption of energy in case of a collision has not been examined so far.
A shock absorber for a two-wheeled vehicle is required to absorb a much larger amount of energy in comparison with that for an automotive vehicle. For example, in the case of an automotive vehicle, kinetic energy to be absorbed Ek=½ mv2 is 102.1 [J], which is determined based on the energy generated when a dummy head of 4.54 kg in mass clashes at a speed of 15 mile/h (=6.71 m/s). In the case of a two-wheeled vehicle, kinetic energy to be absorbed Ek is 9646 [J], where the vehicle mass is 100 kg, and the traveling velocity is 50 km/h (=13.89 m/s). Accordingly, an incommensurably large energy absorption must be realized.
Assuming that a resin rib for an automotive vehicle is used, the height of the rib is in the order of 60 mm at most. Accordingly, a considerably large area is required on the two-wheeled vehicle when the resin rib, having the same absorption stroke, is applied thereto, which is actually impossible. The shock absorber is to be mounted at the front end of the two-wheeled vehicle. Accordingly, it is impossible to enlarge the front area thereof. On the other hand, assuming that a method of increasing the height of the resin rib is employed, the rib may be ever-increasingly thicker because it is necessary to provide a draft angle for manufacturing reasons. This results in a disadvantage in that a generated load increases.